The sea surface microlayer as a source of viral and bacterial enrichment in marine aerosols.

The main source of aerosols from the marine environment are generated by bubbles. These aerosols are easily suspended and transported in the lower atmosphere. Bubbles are created by several sources including rain and boat traffic to name two. When the bubbles are introduced to the water column surface-reactive in-organic and organic compounds as well as small particles which include bacteria and viruses collect on the bubbles surface. The bubbles then rise through the water column and when they reach the surface they burst and eject the collated materials as an aerosol into the atmosphere as well as delivering them to the surface microlayer (SML). The SML is known to be much more microbe rich compared to subsurface waters which can lead to dissolved organic matter (DOM) and particulate organic matter (POM) being enriched up to 1000 times. Bubble scavenging and delivery to the SML is thought to be a likely mechanism for this enrichment. The aerosol particles are thought to be the most enriched, much more than both the SML and subsurface waters. Aerosol formation is also thought to be the main vector for bacteria and virus transport across the air-sea interface. There is some evidence to suggest that the bacteria in the aerosols can remain viable after overland transport for distances of up to 200m.

Sample were collected from sites off the coast of Long Island, New York using a small catamaran to collect SML, subsurface and aerosol samples from in-situ experiments. Aerosol samples were collected over a greater distance by the R/V Seawolf along a 200km transect.

SML samples were collected using the mesh screen method and then the bacteria, Viruses (VLPs) and transparent exopolymer proteins (TEP) where analysed. Bacteria was counted under a microscope after being stained using DAPI and VLP’s using SYBR Gold. TEP was measured using Alcian Blue dye. An experiment was also carried out to differentiate between metabolically active and damaged bacteria.

In the bacteria and VLP enrichment experiments the authors found that bacteria where enriched on average 10 fold in aerosols and 6 fold in the SML. They also found that VLP was enriched on average 10 fold in aerosols and 7 fold in the SML. Base level of abundance was taken from the Subsurface water.

In particle association experiments they found that all 3 of the major particles (TEP, DAPI-stained particles and proteinaceous particles) where enriched by 2 – 5 fold in the SML and 20 – 40 fold in aerosols. In the subsurface water only 11% of bacteria and 17% of the VLPs where associated with particles. IN the SML 23% of bacteria and 15% of VLPs were associated with particles. In aerosols 59% of bacteria and 35% of VLPs were associated with particles.

Metabolically active and undamaged cells declined in number from the subsurface water at around 60% to just 8% in the SML. The authors speculated from this result that rather than being a nutrient rich and stable the SML is a place where phyto- and zooneuston concentrate along with anthropogenic poisons as well as a greatly enriched viral community increasing susceptibility to disease.

This paper gives a good insight into the release of sea born bacteria and viruses in to the atmosphere. It also gives scope to a new study on whether human pathogens can be transported in the same way although it is a fair guess that they could be.

The sea surface microlayer as a source of viral and bacterial enrichment in marine aerosols